Methods of providing article with corrosion resistant coating and coated article

Abstract

According to the invention, an article that is exposed to high temperature e.g., over 1000.degree. C. during operation is disclosed. In one embodiment, a method for a gas turbine engine includes a directionally solidifed metallic substrate, e.g., a superalloy, which defines an airfoil, a root and a platform located between the blade and root. The platform has an underside adjacent the root, and a corrosion resistant overlay coating such as an MCrAlY or a noble metal containing aluminide or corrosion inhibiting ceramic is located on portions or the blade not previously covered with such coatings, e.g., the underside of the platform and the neck. The applied coating prevents corrosion and stress corrosion cracking of blade in these regions. Where the airfoil is also created, the airfoil coating may have a composition different from that of the coating on the underplatform surfaces.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001] Some of the subject matter disclosed herein is also disclosed in commonly owned pending applications Ser. Nos. ______ entitled "Article Having Corrosion Resistant Coating"by Allen, Olson, Shah and Cetel [Attorney Docket No. EH-10365], ______ entitled "Article Having Corrosion Resistant Coating" by Allen and Olson, filed on even date herewith and expressly incorporated by reference herein [Attorney Docket No. EH-10379], and ________ entitled "Article Having Corrosion Resistant Coating" by Shah and Cetel [Attorney Docket No. EH-10384].BACKGROUND OF THE INVENTION[0002] The present invention relates generally to coatings for corrosion protection, and more particularly to methods of applying such coatings to articles.[0003] Gas turbine engines are well developed mechanisms for converting chemical potential energy, in the form of fuel, to thermal energy and then to mechanical energy for use in propelling aircraft, generating electric power, pu...

AI Technical Summary

Benefits of technology

[0009] According to one aspect of the invention, improved durability of gas turbine blades is achieved through application of corrosion resistant coatings. A turbine blade for a gas turbine engine, typically composed of a directionally solidified nickel-based superalloy, including an airfoil, a root and a platform located between the blade airfoil and root. The platform has an underside adjacent the blade neck, and the blade neck is adjacent to the blade root.

[0010] In one aspect of this invention, a corrosion resistant overlay coating such as an MCrAlY (M typically consisting of nickel and / or cobalt) is applied to the underside of the platform and portions of the blade neck. To maximize corrosion protection, the coating should preferably be composed of about 20-40% Cr and 5-20% Al. The presence of this coating improves component life by preventing blade corrosion by the salt accumulating on regions of the blade shielded from direct exposure to the gas path. An additional benefit of the applied coating is the prevention of blade stress corrosion cracking. The corrosion resistant overlay coating prevents corrosion and / or stress corrosion cracking by acting as a barrier between the salt and nickel-based alloy component. The coating system may include an aluminide or platinum aluminide coating layer either between the substrate and the MCrAlY layer or over the MCrAlY layer.

[0011] According to another aspect, a corrosion resistant aluminide coating such as a platinum aluminide coating is applied to the underside of the platform and portions of the blade neck. To maximize corrosion protection, the coating should possess between about 30-45 wt. % platinum, balance aluminum. Additional coatings may be applied over the aluminide, e.g., a metallic overlay or a ceramic insulating layer.

Problems solved by technology

However, providing cooling air reduces engine efficiency.

Since coatings add weight to a part and debits fatigue life, application of the coating is intentionally limited to those portions of the component for which the coating is necessary to achieve the required durability.

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